A synthetic rubber-based hot melt adhesive containing a thermoplastic block copolymer as a main component has widely been used as a hot melt adhesive which is used in disposable products such as a diaper and a napkin and is applied to a base material thereof, for example, a nonwoven fabric, a tissue, a polyethylene film and the like.
In case of producing the disposable products, a film or a nonwoven fabric is coated with a hot melt adhesive, and high-speed coating is sometimes employed so as to enhance the production efficiency of the disposable products. However, the synthetic rubber-based hot melt adhesive may be sometimes scattered when applied at a high speed.
One of means for enhancing the production efficiency of the disposable products includes a method in which an olefin-based hot melt adhesive typified by an ethylene-propylene copolymer is applied at a high speed.
WO 2003/087172 A1, JP 2003-533551 A and JP 2003-518171 A disclose a hot melt adhesive containing an olefin polymer as a main component. It is known that an olefin-based hot melt adhesive is commonly more suitable for use in paper processing than use in disposable products.
WO 2003/087172 A1 discloses that a propylene polymer is used as a raw material for a hot melt adhesive. However, the hot melt adhesive of Patent Literature 1 does not have sufficient adhesion to a polyethylene film. A diaper, a sanitary napkin and the like often have a structure in which an absorber constituted by a pulp, an absorbent polymer and the like is wrapped in a tissue and the outside thereof is covered with a nonwoven fabric, a polyethylene film and the like. Therefore, it is required for the hot melt adhesive for disposable products to have a strong adhesive strength to the polyethylene film.
JP 2003-533551 A discloses a polyolefin-based hot melt adhesive for disposable products. In case of spiral coating of a polyethylene film with the hot melt adhesive of JP 2003-533551 A, it is necessary to decrease the viscosity by increasing a coating temperature so as to cope with a complicated coating pattern. As shown in JP 2003-533551 A, the coating temperature of the hot melt adhesive is set to high temperature (350° F. to 365° F.). However, when the polyethylene film is coated with the hot melt adhesive at the above temperature, the film would be melted and the coated hot melt adhesive would shrink due to cooling, resulting in the formation of wrinkles in the film.
JP 2003-518171 A discloses a propylene-based hot melt adhesive. However, it is also difficult for the hot melt adhesive of JP 2003-518171 A to be applied by spiral coating at low temperature, as is the case with the hot melt adhesive of JP 2003-533551 A, and also it is hardly to say that the peel strength between nonwoven fabrics is sufficient.